SDC1 and plasma cell myeloma: The use of GSI might increase expression of BCMA on the myeloma cell surface while also decreasing the levels of sBCMA in circulation, overall leading to increased efficacy of anti-BCMA CAR T. Novel therapies targeting molecules beyond CD19 and BCMA, including CD4 [56], CD38 [57], CD44v6 [58], CD138 [59], SLAMF7 [60], and others are under investigation (Table 4).